IN a way, Friday night at Celtic Park will be just another game for Aiden McGeady and James McCarthy.

Professional sportspeople are paid handsomely to leave their emotions in the dressing room and go out and do a "job", whether for club or country. But in their quieter moments, rest assured both of these outstanding footballers will have given thought to the ironies of it all.

Having been born in Scotland and shaped by Scotland, they could never have imagined that one day they would also be defined by their performances against Scotland in surely the biggest international match in this country for seven years. Along with the rest of an Irish travelling band replete with Celtic connections such as manager Martin O'Neill, assistant Roy Keane, and players Robbie Keane, Daryl Murphy and Anthony Stokes, these two have it in their power to leave a fair old dent in the Scottish footballing psyche.

The story of why this pair will be in the away dressing room rather than the home one for the Euro 2016 qualifier at Celtic Park requires only the briefest of re-tellings. The first and most important thing to state, of course, is that both men are hugely proud of their Irish heritage. McGeady spent most summers holidaying at his grandparents' in Gweedore, while McCarthy's choice of international allegiance honours the memory of his grandfather Paddy Coyle, from Donegal, who passed away when he was young.

But it is far more complicated than that. Because in truth had SFA practices been sharper there is a fair chance both men could have been donning dark blue instead.

While grainy images exist of McGeady wearing Republic of Ireland strips as a child, he did appear for Scotland Schoolboys, only for the Irish to fill the void when Celtic became so unhappy with the coaching on offer that they withdrew their youth players from the Scottish Schools FA system.

While that loophole was swiftly closed, the mistakes continued. Despite being in the Hamilton Academical first team at the age of 15, McCarthy was simply overlooked by SFA youth team tsar Archie Knox. Right up until Giovanni Trapattoni finally gave McCarthy his first senior Ireland cap, then Scotland manager Craig Levein hadn't given up on persuading him to change his allegiance, but it was a mistake which Scotland were never able to undo.

Perhaps with a word of warning from their international manager, both men were keeping their counsel about their impending date with destiny this week, so it was left to others to do the talking. The Scottish parts of the Celtic Park crowd on Friday are unlikely to spare them, but Steven Naismith, who shares an Everton dressing room with them, along with fellow Republic of Ireland squad members Seamus Coleman and Darron Gibson, feels his opponents will embrace the environment.

"Aiden and James will be looking forward to it," Naismith said. "It is a match we are all looking forward to. But it will be strange for everybody for different reasons. Aiden is coming back to Celtic Park, and then they are playing against Scotland, obviously, which is something they will never have done in their international career. Without a doubt it will be strange for them."

So close do these three Celtic cousins appear on the field, Naismith will find it strange to be on the opposite side from McGeady and McCarthy in a death struggle for Euro 2016 qualification.

"As club-mates we can all play off each other and read each other's runs. It is that understanding which has us playing so well together as a team at Everton," he said. "We haven't been talking about it too much in the dressing room, to be honest, just because there have been so many games."

For Everton, the latest of those matches arrives against Steven Fletcher and John O'Shea's Sunderland today. However Friday night pans out - O'Neill will trim back his provisional 37-man squad after the weekend's games - it is a pretty fair guess that the Goodison Park side's triumvirate of products of the West of Scotland will be heavily involved in the outcome.

"There has been a lot of banter about it," says Sylvain Distin, the club's veteran centre-half. "In their own ways all three of them have integrated very well. They are completely different players, but they all have their own strengths and we need them in our squad.

"What I love about Steven, and he knows this because I have told him, is that he just keeps working. Everybody always wants the guys like Messi and Ronaldo, but you always need a player like Naisy, who maybe has less quality but has a big heart and never stops running. I love this type of player - maybe because I am a bit like this as well.

"James is very consistent. He has a big engine and he just runs and runs. When he gets to my age, he is going to feel it! But you know week in, week out what you are going to get from him and he is very, very safe, very secure in possession and we need that as a team.

"Aiden is lightning sharp, more like that Messi-Ronaldo thing, that spectacular type of player, when one piece of action can change a game.

"I don't think it is going to change anything if they are booed. You are used to getting abuse when you go to places like Anfield.